Michael: We have a 16K Reece for our LB Dodge pulling a 2955RL and it works fine. I don't agree with Dave on the side to side motion. I feel I have more stability not having the lateral pitch, but to each his own.
Also I don't know of any 5th wheels that bolt only to the bed. Most need to have the frame of the truck drilled and brackets put under it to support the weight. And when I take my 5th wheel out, the rails are still on the floor.